1. Field of the Invention
This invention relates to fluid mixtures of anionic and nonionic surfactants, and to processes for converting them into detergent powders.
2. The Related Art
Recent trends in the detergents market are towards denser fabric washing powders. The reasons for this are partly due to reduced packaging costs coupled with environmental considerations relating to less packaging materials. The majority of commercial detergent washing powders are presently manufactured by spray-drying processes which inherently tend to produce powders of relatively low bulk density, typically less than 500 g/liter. The bulk density of such powders is directly dependent on the amount and type of active detergent present in the powder during the spray-drying operation.
The commonly used anionic detergents, such as, sodium alkyl sulfates and sodium alkyl aryl sulfonates, are particularly prone to produce light powders by spray-drying methods.
Powders with higher bulk densities can be obtained if part of the active detergent is post-dosed onto the spray-dried powders rather than incorporated into the slurry before spray-drying. However, in order to be suitable for post dosing by spraying onto the powders, the active detergents (surfactants) must be sufficiently mobile to be atomized effectively at temperatures low enough to prevent degradation of the active, i.e., below about 90.degree. C.
GB Patent No. 1 279 261 relates to processes for converting various liquid or liquefiable detergents principally nonionics into detergent powders by spraying those surfactants onto spray-dried builder beads. However, mixtures of aqueous anionic and nonionic surfactants are generally viscous gels which can only be oversprayed onto particulate absorbents if they are heated to a temperature, typically above 90.degree. C., at which they become sufficiently mobile. This temperature in turn produces severe disadvantages in factory practice.
EP No. 88612A discloses mobile liquid detergents containing not more than 8% water and not less than 90% active detergent, including an anionic surfactant, a nonionic polyether, and coconut mono- or diethanolamide. Substantial quantities of the ethanolamide are required in order to obtain sufficiently mobile liquid products.
French Patent 2,645,876 discloses a combination of alkylbenzene sulfonate, nonionic and optionally ammonium quaternaries and water.
GB Patent No. 1,169,594 discloses liquid detergent compositions containing ammonium alkylbenzene sulfonate and a nonionic detergent. The compositions are prepared by passing ammonium through a mixture of alkylbenzene sulfonic acid and nonionic detergent.
U.S. Pat. Nos. 4,826,632 and 4,923,636 and European Patent 0,265,203 all disclose mobile liquid detergent compositions consisting essentially of up to 80% of selected anionic surfactant (sodium or potassium alkylbenzene sulfonate and/or alkyl sulfate), up to 80% selected nonionic surfactant and water in an amount not exceeding 10% by weight. These disclosed mixtures lose mobility as the water content increases over 10%.
U.S. Pat. No. 5,045,238 discloses a process for making high active alkyl sulfate paste and particles, nonionic may be included. In preparing these a slight excess of the stoichimetric amount of caustic NECESSARY to neutralize the alkyl sulfuric acid is employed up to a maximum of 1.5%. According to the patent, excess over this amount results in viscosity too high to pump easily.
An object of the present invention is to overcome one or more of the disadvantages of the art. Other objects will become apparent through the following summary, detailed discussion and examples.